Light-developable photographic material and recording process



United States Patent O 3,508,921 LIGHT-DEVELOPABLE PHOTOGRAPHIC MATE-RIAL AND RECORDING PROCESS Paul Desire van Pee, Edegem, and Jozef FransWillems,

Wilrijk-Antwerp, Belgium, assignors to Gevaert-Agfa N.V., Mortsel,Belgium, a Belgium company No Drawing. Filed Oct. 11, 1966, Ser. No.585,733 Claims priority, application Great Britain, Oct. 11, 1965,42,373/ 65 Int. Cl. G03c /32 US. Cl. 9645.2 22 Claims ABSTRACT OF THEDISCLOSURE Photographic elements are described which comprise aradiation-sensitive silver halide emulsion layer of the lightdevelopabletype applied from a coating composition containing (1) a silver iodidesol and/or a compound which will release iodide ions, and (2) at leastone halogen acceptor corresponding to the following general formulawherein:

each of R R R and R is hydrogen, an alkyl radical or an aryl radical, or

R and R and/ or R and R together are the atoms necessary to close aheterocyclic ring, and

n is an integer from 1 to 4.

The photographic element has application in light-development recordingand the like.

The present invention relates to photographic elements comprising animproved light-developable radiation-sensitive silver halide emulsionlayer, as well as to a process for making records employing saidelements.

The light-developable silver halide materials have become of increasinginterest, for they possess desirable properties for high speedrecording, such as high speed oscillographic recording of events, whichoccur in rapid sequence, and the like.

Light-developable silver halide materials for direct recording areradiation-sensitive materials in which a visible image can be obtained,after an exposure to a high intensity source of radiation has beeninitially utilized to form a latent image, by an additional exposure toa radiation of lower intensity such as diffuse daylight or artificiallight. The secondary enclosure, also called latensification, is anoverall exposure, including exposing the areas in which the initiallatent image was formed as well as the surrounding background to anadditional amount of radiation.

It is known that in general, intense exposure favours the formation of alatent image in the interior of the grains while low-intensity exposureforms almost exclusively a surface latent image. The surface latentimage is the one developed by a usual chemical development Whereas theinternal latent image is practically not developed by such processing.The light absorbed by the silver halide in the secondary exposureprovides the energy for the development of the internal latent image toa visible form (cf. H. Hunt High Speed Direct Recording Papers, Phot.Sci. Eng, vol. 5, No. 2, 1961).

Many of the known light-developable, radiation-sensitive materials havethe disadvantage that on latensification the image becomes very slowlyvisible, that the background tends to darken fast and that the maximumdensity of the image decreases on a prolonged secondary exposure.

It has now been found that the addition of at least one 3,508,921Patented Apr. 28, 1970 member selected from a silver iodide sol and acompound that sets free iodide ions together with at least onehalogen-acceptor corresponding to the following general formula:

each of R R R and R represents a hydrogen atom, an alkyl radicalincluding a substituted alkyl radical, an aralkyl radical and asubstituted aralkyl radical, or an aryl radical including a substitutedaryl radical, or

R and R and/ or R and R together represent the atoms necessary to closea heterocyclic ring including a substituted heterocyclic ring, and

n is an integer from 1 to 4,

to light-developable radiation-sensitive silver halide emulsions resultsunexpectedly and surprisingly in the production of a light-developablematerial in which an improved image can be obtained, showing afavourable contrast between the image and the background (i.e. having agood net density) and having a very good stability as well as a goodchemical developability. As will be seen from the examples hereinafter,the effect of the simultaneous addition of the above compounds is muchmore important than the effects obtained on the one hand by the additionof the halogen acceptor alone and on the other hand by the addition ofthe silver iodide sol and/or the compound splitting oif iodide ionsalone. When only a member of one of these two groups of compounds isincorporated into the light-developable radiation-sensitive emulsionlayer the difference between the maximum and minimum density isconsiderably lower than when both groups are present together. Thisadditive eifect is the more surprising since it was found that thiseffect could not be obtained in the case of a combination of a compoundsetting free iodide ions with many other generally known and often usedhalogen-acceptors e.g. hydrazothiocarbonamide, thiosemicarbazide andthiourea.

The improved light-developable radiation-sensitive photographic silverhalide elements according to the present invention permit a rapid accessto and prolonged examination of the image formed on photodevelopment andalso permit a chemical development and fixing treatment in order toobtain permanent records of the traces or images. The material accordingto the present invention shows a high degree of sensitivity to the tracebeam coupled with a highly stable background i.e. a background which isnot very sensitive to low intensity radiation, thus resulting in amaximum contrast between the image and background. Thus, the images ortraces obtained on lightdevelopment with elements according to thepresent invention are characterized by a high net density, i.e. anoptimum contrast between the image and background, a good resistance tofogging of the non-image areas even when exposed for a long time toambient lighting and even when no chemical development occurs. Ofcourse, when the traces or images produced on latensification areexposed to ambient lighting for a long time the background darkensslowly, however, the contrast between image and background will remainfor many hours. The images or traces will not remain visible whenpermanently exposed to light. To keep a permanent record of the tracesor images, the material has to be chemically developed and fixed,preferably not too long after the light-development. Without saiddevelopment and fixing step, the record will remain permanently onlywhen the lightdeveloped images are exposed to light infrequently andkept in the dark when not in use. Indeed, the image will lastpractically indefinite if protected from prolonged exposure to stronglight.

Another advantage oifered by the light-developable elements of theinvention is that it is possible to carry out the light-developmentwhile supplying heat, whereby the recorded image becomes almostimmediately visible for the reason that, when heating, it is possible toincrease the light-intensity of the secondary exposure without producingfog. A probable explanation of this phenomenon has been given by Jacobs,Phot. Sci. & Eng, vol. 5, No. 1, 1961. By the fact that when operatingat elevated temperature a more rapid image access is obtained, it is notnecessary in those instances where there is recorded at high writingspeeds and thus at high paper transport speeds, to expose considerablemeters of paper to ambient light at the same time, which would lead to ahandling problem. Some oscillographs operate according to thisprinciple: after the high-intensity exposure the print-out material ispassed over a heated plate While being exposed to fluorescent U.V. lampsso that a visible image is produced almost immediately.

The following is a non-restrictive list of halogen acceptors, which haveproved to be particularly suitable for use according to the presentinvention, and which correspond to the above general formula:

(1 Bis-(dimethyl-thiocarbamoyl) -sulphide ao g (2)Bispiperidino-thiocarbonyl)-su1phide CH2C H2 CH2C H2 NC-SCN CH2 (3 Bis-(dimethyl-thiocarbarnoyl) -disulphide Q- -tt- Q S S (7) Bis-(piperidino-thiocarbonyl)-disulphide CHzCH2 CH2C H2 HzC \CH2-C2 S S (8)Bis- (ethyl-phenyl-thiocarbarnoyl) -tetrasulphide CHz-CH GHz-GHa (9)Bispiperidino-thiocarbonyl) -tetrasulphite CHr-CHz CHz-G H2 H2ONCS--SSSON CH2 CH2C2 CHzOI z i l The amount of halogen acceptoraccording to the above general formula that is incorporated into thesilver halide 75 4 emulsion layer according to the present invention mayvary within very wide limits viz. from about 0.01 g. to about 20 g. permole of silver halide, but is preferably comprised between about 0.1 g.and about 5 g. per mole of silver halide.

According to the invention, the halogen acceptors corresponding to theabove general formula may also be used together with other halogenacceptors. Very good results have been obtained when using incombination with the halogen acceptors of the present invention thehalogen acceptors described in our co-pending application entitledLight-Developable Photographic Material and Recording Process filed oneven date herewith.

Suitable compounds setting free iodide ions are among others inorganicand organic iodides, organic compounds with labile iodine atom an oniurnchloroiodates.

Suitable inorganic iodides are for instance the following water-solubleiodides:calcium iodide, ammonium iodide, lithium iodide, magnesiumiodide, potassium iodide and sodium iodide.

Suitable organic iodides are for instance the iodides having thefollowing structural formulae:

l-methyl-8-hydroxy-quinolinium iodide 1-methyl-2-iodo-quinolinium iodide1,2,3,4-tetrahydro 8 hydroxy-l,l-dimethyl-quinolinium QLCHPQ Qbenzyltriphenylphosphonium iodide H3 0 CH3S-S-bis-(dimethyl)-hexamethyleen 1,6 disulphonium iodide C O CH ICIz"trimethyl(o-methoxycarbonyl-anilinium) dichloroiodatebenzyltriphenyl-phosphonium dichloroiodate.

Instead of or in addition to a compound setting free iodide ions, asilver iodide sol comprising an appropriate protective colloid can beadded with the same effect to the silver halide emulsion. A verysuitable silver iodide sol can be prepared by slowly adding whilestrongly stirring the following solution A to the following solution B,both solutions being heated to 35 C.

Solution A 3 N AgNO -l7 ccs. Water up to 1 litre Solution B 3 N KI-l7ccs. Gelatin 40 g.

Water up to 1 litre The amount of compound setting free iodide ions mayalso vary within very wide limits. In general an amount from about 0.01g. to about 20 g., preferably from about 0.1 g. to about g. per mole ofsilver halide is applied. The same applies to the limits within whichthe silver iodide sol is used. In the latter case the above amountsrelate to the silver iodide and not to the total sol. The addition of amember selected from a silver iodide sol and at least one compoundsetting free iodide ions, and preferably also the addition of thehalogen-acceptor occurs after the emulsion preparation and preferablyjust before coating on a suitable support. Except the addition of thesilver iodide sol, any other addition can occur from a solution of thecompound involved in a suitable solvent, which is mostly water but mayalso be an organic solvent.

By the addition to a silver halide emulsion of a compound setting freeiodide ions or of a silver iodide sol, silver iodide is produced on thesurface of the silver halide grains of the emulsion, in the former caseby conversion and in the latter by adsorption. The formation of silveriodide at the surface of the grains and the favourable effects resultingtherefrom for the method of the present invention can also be attainedby conducting the emulsion layer obtained after coating through asolution, preferably an aqueous solution of a compound setting freeiodide ions, or by treating this emulsion layer in some other waytherewith.

According to the invention any silver halide emulsion of thelight-developable type may be used. These kinds of emulsions are verywell known to those skilled in the art. They mainly or entirely form aninternal latent image and only to a little extent an external latentimage.

A silver halide emulsion that mainly or entirely forms an internallatent image and only to a little extent an external latent image is anemulsion in which only few or no exposed grains at all are developableinto silver by a developing solution that cannot act as a developer fora latent image inside the grains i.e. a so-called surface developer,such as:

p-Hydroxyphenyl glycine-40 g. Sodium carbonate (cryst.) g. Water to 1000ccs.

and wherein the exposed grains are well developable to silver by adeveloping solution that acts as a developer for latent image inside thegrains, i.e., a so-called internal developer such as the followingsolution:

Hydroquinone-15 g.

Monomethyl-p-aminophenol sulphatel.5 g.

Sodium sulphite (anhydrous)-50 g.

Potassium bromide-10 g.

Sodium hydroxide-J5 g.

Sodium thiosulphate (cryst.)-2O g.

Water to 1000 ccs.

By a silver halide emulsion that mainly forms internal latent image andlittle external latent image there is more particularly meant a silverhalide emulsion, a test layer of which upon exposure to a lightintensity scale for a fixed time between and 1 sec. and development for3 min. at 20 C. in the above internal developer, exhibits a maximumdensity at least 5 times the maximum density obtained when an identicaltest layer of the said silver halide emulsion is equally exposed andthen developed for 4 min. at 20 C. in the above surface developer.

Silver halide emulsions that meet the above requirement and hence aresuitable for being employed in the process of the invention aregenerally not or only slightly chemically ripened silver halideemulsions, since the extent of the surface latent image-formingcapability increases with the degree of chemical ripening.

Silver chlorobromide and silver bromide emulsions have proved to bespecially suitable for the purpose of the invention. When theseemulsions comprise minor amounts of silver iodide, preferably not morethan 5 mole percent relative to the total amount of silver halide, theyare just as well suitable.

The silver halide emulsions for use in the present process are generallygelatin silver halide emulsions. However, the gelatin may wholly orpartially be replaced for instance by another protein, a hydrophilic notproteinaceous colloid or a synthetic polymeric substance applied from anaqueous dispersion. The light-sensitive silver halide emulsions may beprepared according to all known and conventional techniques for emulsionpreparation. A method according to which emulsions are prepared, andwhich has proved to be particularly suitable for the purpose of theinvention, is the so-called conversion method according to which anemulsion of a silver salt that has a higher degree of solubility thansilver bromide is converted into a silver chlorobromide or a silverbromide emulsion that occasionally contains small amounts of silveriodide. This conversion is carried out preferably very slowly forinstance by several consecutive steps.

The emulsions can, if desired, be modified prior to coating by theaddition of all kinds of ingredients, which are generally known in theart of emulsion preparation and some of which will be set outspecifically hereinafter. Among the said ingredients may first bementioned the common additives for light-sensitive silver halidematerial such as hardening agents, e.g., formaldehyde, coating aids,e.g., saponine, plasticizers, e.g., glycerol, optical sensitizers of theclass of the cyanine dyes, the merocyanine dyes, etc., developmentaccelerators, compounds that render the material more resistant towrinkling and less brittle etc. Further, more specific ingredients maybe incorporated also. Among these may be mentioned more particularly:

Thiocyanates, such as potassium thiocyanate, which further stabilize thelight-developed image;

Compounds or mixtures of compounds reducing the background density onlatensification, e.g., lead salts, and preferably cadmium salts; thesesalts are preferably salts that are water-soluble such as lead acetate,lead iodide, lead nitrate, cadmium iodide, cadmium chloride, cadmiumbromide, cadmium nitrate, etc.;

they give rise to a decrease of the minimum density without, however,decreasing the maximum density to the same extent so that as a resultthereof the contrast is enhanced. Said salts may be added to theemulsion during the emulsion preparation or the conversion of the silversalt emulsion by means of a bromide as well as just before coating theemulsion on a support. They are added in amounts varying from about 1 g.to about 20 g., preferably from about 5 g. to about g. per mole ofsilver halide.

The amount of gelatin applied in emulsion making is preferably such thatper kg. of emulsion ready for coating from about g. to about 150 g. ofgelatin is present.

The amount of silver nitrate used in emulsion making preferably variesfrom about 50 to about 200 g. per kg. of emulsion.

The emulsion is generally coated in such a way that 1 kg. of emulsioncovers approximately from about 20 to about sq. m. of support.

Suitable supports for the elements of this invention include theflexible supports used in the prior art for lightwriting andoscillographic recording. They may be any type of paper, as well asfilms of cellulose nitrate, cellulose acetate, poly(vinyl acetal),polystyrene, poly(ethylene terephthalate) and other synthetic resins.Supports of glass, metal, and other substances are not excluded. In thisconnection conventional photographic base papers may be convenientlyutilized.

In order to form an image in the light-developable radiation-sensitivephotographic elements according to the present invention, said elementsare first exposed to a high-intensity actinic radiation, e.g., fromxenon tubes, U.V. lamps or high-pressure mercury arc lamps as used incertain oscillographs.

The high-intensity radiation source used for the initial or firstexposure of the light-developable material is generally rich in blue andultraviolet radiation but said radiation may be any light or otherelectromagnetic radiation of either visible or invisible wave length,X-rays, gamma rays or an electron beam. After the initial exposure thematerial may be light-developed by exposure to low intensity daylight,incandescent light or fluorescent light, or by the use of photofloodlamps as commonly used in photography. This secondary exposure must notnecessarily be performed with the aid of an actinic radiation source.When light-developing with common ofi'lce lighting or daylight the imagebecomes visible after 15-30 seconds, attaining maximum density inseveral minutes. In certain instances i.e. for obtaining practicallyimmediately visible traces or images it may be advantageous, as alreadystated above, to carry out the development While supplying heat.

This can be carried out by running the material over a hot plate at -180C. in the secondary exposure step.

The sharpness of the recorded trace or image may be further increased bya short preliminary exposure of the light-developableradiation-sensitive material according to the invention to ordinarylight e.g. daylight, prior to exposing the material to thehigh-intensity radiation. Indeed, by this short preliminary exposure thegradation in the toe of the characteristic curve and the contrast or netdensity of the recorded trace or image are increased.

If desired the material may be chemically developed and fixed before,during or after the photo-development, latensification, or secondaryexposure. This development is of the internal type which means that ittakes place in the presence of an energetic silver halide solubilizingagent, e.g. sodium thiosulphate, which is mostly present in thedeveloper itself. Said chemical development advantageously occurs in thepresence of an anti-fogging agent. The halogen acceptor used canfunction as such at least when it possesses good antifogging properties.The anti-fogging agent may be incorporated in at least one of thecomposing layers of the photographic element used and/or in thedeveloper. Examples of suitable antifogging agents areZ-mercapto-ethyl-carbanilate, l-phenyl- 2-tetrazoline-5-thione and4,5,6,7-tetrabromo-lH-benzotriazole.

It was noticed that the advantage of the chemical development oflight-developable silver halide material in the presence of anti-foggingagents does not only apply to the material according to the presentinvention but also to any photographic material of the light-developabletype.

Example 1 A light-sensitive photographic silver bromide emulsion of thelight-developable type, i.e. that mainly forms an internal latent imageand only to a little extent an external latent image is prepared byconversion of a silver chloride emulsion into a silver bromide emulsion.Said silver bromide emulsion is prepared so that an amount of silverbromide equivalent to g. (0.7 mole) of silver nitrate is present per kg.of emulsion. The usual emulsion ingredients and coating aids areincorporated into the emulsion, and in addition thereto anorthochromatic sensitizing agent, and 8 g. of cadmium bromide per kg. ofemulsion for reducing the background density.

The emulsion obtained is divided into many different emulsion samples.To these samples are added the addi tives according to the invention aslisted in the table hereinafter. The halogen-acceptor is added in anamount of 40 cos. of a 1% by Weight solution in a suitable solvent perkg. of emulsion whereas the compound setting free iodide ions, in thisparticular case potassium iodide, is added in an amount of 10 cos. of a4% by weight aqueous solution per kg. of emulsion.

All emulsion samples obtained are coated on conventional photographicpaper supports such that an amount of silver halide equivalent to 4 g.of silver nitrate is present per sq. m. of light-sensitive material.

All light-sensitive materials obtained are subjected to the followingidentical successive treatments:

(1) They are exposed in a fiash-sensitometer Mark VI of Edgerton,Germeshausen and Grier for 10- sec. through a step wedge with a constantof 0.3.

(2) The exposed materials are photo-developed for 15 min. by exposure toordinary office fluorescent lights with a total light intensity of 240Lux whereupon the density of the image-areas and non-image areas aremeasured in a MacBeth reflection densitometer. The difference betweenthe maximum and minimum density AD of all materials is listed in thetable hereinafter.

(3) In order to determine the stability of the image, the differencebetween the maximum and minimum density AD is measured again afterlatensification in analogous circumstances as in (2) but for 10 hours.

9 This difierence AD of all materials is also listed in the tablehereinafter.

TABLE Material Additive AD AD 1 None 0. 12 0. 09 2. KI alone O. 36 0.203- s- Compound 1 alone- 0. 29 0.19 4 Compoundl +KI.-- 0.43 0.23 0. 33 0.18

Compound 9 +KI. 0. 40 0. 24

Example 2 The process of Example 1 is repeated with the difference thatas compounds setting free iodide ions and as halogen-acceptors accordingto the above general formula are used the compounds listed in the tablehereinafter. Only the AD values after 15 min. of photodevelopment havebeen measured. In the last column of the table are listed the number ofsteps of the wedge that are recorded. This number is a measure of therelative sensitivity of the different radiation-sensitivephoto-developable materials.

Number Material Additive AD of steps 0. l2 6 0. 29 6 3 Mono-iodo aceticacid 0. 3O 6 4 Compound 1+mono-iodo acetic 0.39 7

ac 5 3,5-dimorpholino-di-thiolium 0. 28 6 iodide. 6 Compound l+3,5-dimorpholino- 0. 36 7 di-thiolium iodide.

As can be seen from the results listed in the above table the materialscomprising a compound setting free iodide ions or a halogen acceptoralone, show less difference between the image and background densities,than the materials comprising both a compound setting free iodide ionsand a halogen acceptor; thus the contrast between image and non-imageareas is enhanced.

Example 3 A light-sensitive photographic silver bromide emulsion of thelight-developable type is prepared as described in Example 1. Theemulsion obtained is now divided into 3 samples A, B and C. To emulsionsamples B and C is added per kg. of emulsion as anti-fogging agent 5ccs. and 15 ccs. respectively of a 5% by weight solution in ethanol ofl-phenyl-Z-tetrazoline-S-thione. To sample A no antifogging agent isadded.

Before coating in the way as described in Example 1 each emulsion sampleon a conventional photographic paper support 40 ccs. of a 1% by weightsolution of bis-(dimethylthio-carbamoyl)-sulphide in ethylene glycolmonomethyl ether and 10 ccs. of a 4% by weight aqueous solution ofpotassium iodide are added per kg. of emulslon.

Each of the 3 materials obtained is exposed to high intensity-radiationas described in Example 1, and photodeveloped by exposure for 20 min. toordinary ofiice fluorescent light with a total light intensity of 240Lux.

Immediately thereafter the samples are developed at 20 C. for 1 /2 min.in an internal developer with the following composition:

Hydroquin0ne6 g. Monomethyl-p-aminophenol sulphate3 g. Sodium sulphite(anhydrous)30 g. Potassium bromide-2.5 g.

Sodium carbonate (anhydrous)-50 g. Sodium thiosulphate (cryst.)10 g.

Water to 1000 ccs.

The samples are then fixed, rinsed and dried in the usual way.

After development the image densities and background densities of eachof the materials are determined and listed in the following table.

Sample Maximum density Minimum density AD A 1.31 1. 17 0. 14 B 1. 28 1.05 0. 23 C 1. 23 0. 0. 28

From this table it appears that by the addition of an anti-fogging agentthe maximum and minimum densities both decrease, the background-density,however, decreasing more markedly than the image-density. Thus, the

difference between maximum and minimum density, i.e. the net density,increases when an anti-fogging agent is added.

Example 4 Max. Min. Material Additive dens. dens. AD

1 O. 42 0. 26 0. 16 2 35 cos. of solution of 1 g. of 0. 65 0. 34 0. 31

compound 1 in ccs. of

ethylene glycol monomethyl ether. 3 100 g. of silver iodide sol pre- 0.80 0. 43 0. 37

pared as described herein. 4 Both said additives oi the 0. 82 0. 40 0.42

materials 2 and 3 together.

As can be seen from the above results, the materials into whichhalogen-acceptor or silver iodide sol alone has been incorporated showless difference between the image and background densities than thematerials to which both halogen-acceptor and silver iodide sol have beenadded. Thus, the contrast between image and nonimage areas has beenenhanced.

We claim:

1. Photographic element comprising a radiation-sensitive silver halideemulsion layer of the light-developable type, applied from a coatingcomposition containing in addition to said silver halide emulsion 1) asilver iodide sol and/or a compound which will release iodide ions, and

(2) at least one halogen acceptor corresponding to the following generalformula:

1 1 wherein:

each of R R R and R is hydrogen, an alkyl radical or an aryl radical, or

R and R and/or R and R together are the atoms necessary to close aheterocyclic ring, and

n is an integer from 1 to 4.

2. Photographic element according to claim 1, wherein said compoundwhich releases iodide ions is an organic or a water-soluble inorganiciodide.

3. Photographic element according to claim 2, wherein said water-solubleinorganic iodide is potassium iodide.

4. Photographic element according to claim 1, wherein the silver iodideof the sol and/or the compound setting free iodide ions is present in anamount of from 0.1 to S g. per mole of silver halide.

5. Photographic element according to claim 1, wherein thehalogen-acceptor is present in an amount of from 0.1 to 5 g. per mole ofsilver halide.

6. Photographic element according to claim 1, wherein said emulsionlayer is essentially a silver bromide emulsion layer.

7. Photographic element according to claim 1, wherein said emulsionlayer also comprises a cadmium and/ or a lead salt.

8. Photographic element according to claim 7, wherein said salt iscadmium bromide.

9. Photographic element according to claim 7, wherein said salt ispresent in an amount of from about 5 g. and 15 g. per mole of silverhalide.

10. Photographic element according to claim 1, wherein said emulsionlayer also comprises a thiocyanate.

11. Photographic element according to claim 10, wherein said thiocyanateis potassium thiocyanate.

12. Photographic element according to claim 1, wherein said emulsionlayer also comprises an anti-fogging agent.

13. Photographic element according to claim 12, wherein saidanti-fogging agent is 1-phenyl-2-tetrazoline- S-thione.

14. Photographic element according to claim 1, wherein said emulsionlayer also comprises an optical sensitizing agent.

15. Photographic element according to claim 1, wherein thehalogen-acceptor is added to the radiation-sensitive coating compositionjust before coating.

16. Photographic element comprising a radiation-sensitive silver halideemulsion layer of the light-developable type, the silver halide grainsof which comprise silver iodide at their surface, said emulsion layercontaining at least one halogen-acceptor corresponding to the followinggeneral formula:

wherein:

each of R R R and R is hydrogen, an alkyl radical or an aryl radical, or

R and R and/or R and R together are the atoms necessary to close aheterocyclic ring, and

n is an integer from 1 to 4.

17. Process for recording traces or images comprising exposing to a highintensity actinic radiation a photographic element according to claim 1and light-developing the latent image formed by said initial exposure byoverall exposure of said element to a radiation of lower intensity.

18. Process according to claim 17, wherein an internal development stepand a fixing step are included before, during or shortly after saidlight-development.

19. Process according to claim 18, wherein the development step takesplace in the presence of an antifogging agent.

20. Process according to claim 19, wherein said antifogging agent is1-phenyl-2-tetrazoline-5-thione.

21. Process according to claim 17, wherein said lightdevelopment iscarried out while applying heat.

22. Process according to claim 21, wherein said heat is supplied byrunning the element over a hot plate heated at -180 C.

References Cited UNITED STATES PATENTS 3,226,232 12/1965 Dersch et a1.96l07 X 3,287,137 11/1966 McBride 96-l07 NORMAN G. TORCHIN, PrimaryExaminer A. T. SURO PICO, Assistant Examiner US. Cl. X.R. 96107

